Better name for repository (?)

I recently updated chosen-rails with the koenpunt fork. I love the `update-chosen` task, very convenient. I had two missteps due to the `remote` argument.

1. I thought it meant a git remote, so I used `git remote add`, no go.
1. After looking at the Rakefile, I realized it wanted a repository. I used the GitHub Clone URL button (home page of each repo). That didn't work either.

After looking at the Rakefile again, I realized that it wanted the URL without the .git at the end. Then things worked. Great.

I don't feel strongly about this change – or the specific argument name `repository_url`. Use it if you think it would help.